This tube indirectly modifies routing behavior. For the purposes of routing objects to the nearest valid destination, a single Restriction Tube acts as if it was 5000 blocks long. Items will therefore usually only be routed through it if there is no other way to go.
This means that if you are routing a constant stream of items into any storage block, it will first go with the regular Pneumatic Tube or Redstone tube. The restriction tube allows this as a second way out, since the longer the tube is, the lower the priority. If a chest were to be full, it would act as a last resort.
This recipe is shapeless.